Spiral flow baffle system



Feb. 15, 1966 c. D. SMITH 3,235,003

SPIRAL FLOW BAFFLE SYSTEM Filed June 4, 1965 2 Sheets-Sheet 1 .AGE

INVENTOR. C/ aV Q sSkv/774,

Feb. 15, 1966 c. D. SMITH 3,235,003

SPIRAL FLOW BAFFLE SYSTEM Filed June 4, 1963 2 Sheets-Sheet 2 .9 3053- 30,0) 302 306 V warum l 150631 l Il l. 504 Il f v vuil/v'.- -4 i X- r .I ,A l

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INVENTOR. 0.40m 544/71/ /VEV nited States Patent O 3,235,003 SPIRAL FLOW BAFFLE SYSTEM Cloyd D. Smith, 14928 La Cumbre Drive, Pacific Palisades, Calif. Filed June 4, 1963, Ser. No. 285,367 5 Claims. (Cl. 165-135) This invention relates generally to ow-direction-controlling devices for fluids and particularly to unique spiralilow-inducing baille structures for fluid conduits, and the like, and to fluid ilow devices embodying such baille structures. A number of typical applications of spiral-flowinducing baflle structures in accordance with the invention will be disclosed.

In many fluid systems, it is desirable or essential that a iluid ilowing through a conduit traverse a spiral or helical ilow path. For example, so-called static centrifugal separators are known in the art wherein a fluid, which may be a liquid, a vapor, or a gas, is directed through a conduit containing bailles that are arranged to cause the iluid to follow such a spiral llow path. As a consequence of the rotational component of motion, or swirling motion, of the lluid, the latter` is subjected to a centrifugal force which drives relatively dense substances entrained in the fluid toward the conduit wall, where such substances are collected or withdrawn. Fluid emerging from the separator is thereby relatively free of such substances. A separator of this kind may be used, for example, to separate liquid from a gas or vapor, solid matter from either a liquid or a gas, a relatively dense iluid from a fluid of less density, and so on.

Another kind of iluid ilow device in which spiral fluid flow is desirable is a so-called straight-through muiller for an internal combustion engine. Muillers of this kind are known in the art, for example, wherein spiral ilow of exhaust gas traveling through the muillers is induced by bailles in the muiller exhaust passage. In these rnutllers, the bailles serve a vdual function. First, they induce spiral exhaust gas flow through the muillers. This spiral ilow is desirable since it increases the effective length of the exhaust gas ilow path through the muiller and, thereby, the effective residence time of the exhaust gas within the muiller. Improved attenuation of objectionable acoustic energy present in the exhaust gas is thus attained. The second function of the baffles is to break up the acoustic Wave pattern in the exhaust gas stream and to reflect the acoustic energy waves in the exhaust stream into the surrounding acoustic attenuation means or treatment of the muiller, to wit, acoustically absorbent material and/ or acoustic attenuating chambers surrounding the exhaust gas passage.

The present invention also has application in the field of heat exchange, such as to water heaters. In the conventional case of a straight hot air tube running through a water tank, for example, a heat insulating boundary layer of stagnant air is formed on and clings to the inside surfaces of the hot air tube. Not only does this boundary layer serve as a heat insulating illm, reducing the rate of heat transfer from the hot air in the tube to andy through the wall of the tube to the water on the outside, but it reduces the velocity of hot air flow adjacent the tube Wall, so there is a velocity gradient from the Wall of the tube to the center or core region of the tube where the hot air ilow attains its maximum ilow velocity. The relatively low velocity of the air stream 4adjacent to the boundary layer means failure to achieve optimum scrubbing against the boundary layer, and thus removal thereof, and the resulting retention of the boundary layer means, in turn, that the heat transfer rate otherwise attainable is not realized. Also, as mentioned, the heated central core region of the air ilow through the tube is at maximum velocity, while outside this central core region, the ilow 3,235,063 Patented Feb. l5, 1966 velocity is reduced, and flow velocity at the tube walls is minimized. The air in the outer regions of the tube is thus resident in the tube for longer times, less heat flows through thtse regions per given unit of time, and the temperature in these regions is, therefore, reduced. The air flowing through the tube is thus stratified temperaturewise, with the coolest air unfortunately nearest the tube Wall. Use of spiral ilow bailles in the hot air tube improves the rate of heat transfer very measurably by providing a longer ilow path of the hot air over the tube surfaces, and thereby affording added opportunity for the heat exchange process to occur. Moreover, the spirally directed hot air stream is effective to scrub away the heat insulating boundary layer, and thereby improve heat transer. tions, it is desirable to provide a spiral baille structure which will afford a long ilow path, which will mix the air, so as to avoid unfavorable temperature stratification, and which will act to scrub away the stagnant boundary layer on the tube Wall.

In the past, baffles for inducing spiral iluid ilow in conduits have typically -comprised a conventional helix, such as a helically twisted metal strip or vane, or a helical structure which is formed in some other similar way. A helical baille of this kind, however, is deficient in several respects. For example, such a baflle is diillcult to form, Further, the helically twisted baille is awkward to handle and to insert into a close-fitting iluid passage. Other more serious ldeficiencies of the existing spiral-ilow-inducing helical bailles reside in the fact that only a relatively small portion of the total surface area of these baflles is effective to reflect incident acoustic wave energy and in the fact that the bailles comprise only a single spiral. As a result, only one spiral ilow path through the baille is provided, whereby the baflle may create excessive back pressure in the iluid stream in which it is placed. The existing baiiles of this type are also costly to make.

A general object of the present invention is to provide unique spral-flow-inducing baille structures for fluid conduits and the like which avoid deficiencies inherent in existing baille structures for this purpose and which have new and useful properties such as longer flow path, improved mixing, and low back pressure.

Another object of the invention is to provide baille structures of the character described which are uniquely designed for simplicity and economy of manufacture and efficiency of operation.

A more speciiic object of the invention is to provide baflle structures of the character described having a unique, open, multi-spiral configuration, whereby a plurality of spiral ilow paths are provided through the baille structures and the latter create minimum back pressure in the iluid stream in which they are placed as well as long flow path.

A further object of the invention is to provide specific iluid ilow devices embodying the present improved baille structures, to wit, but without limitation, a static centrifugal separator, a muiller, an acoustic filter, and a heat exchanger.

Yet a further object of the invention is to provide spiral-ilow-inducing baflle structures of the character described which are uniquely designed for fabrication from sheet material, or by molding or casting, or by other conventional manufacturing techniques.

Other objects, advantages, and features of the invention will become readily evident to those skilled in the art as the description proceeds.

Briefly, the objects of the invention are attained by providing baille structures made up of at least one, and in most cases a multiplicity of, axially spaced baille plate sets, each including at least a pair of crossed baille plates. The baille plates of each plate set are disposed in inter- It will be seen that, in such heat transfer applicasecting planes inclined in opposite directions from a plane containing the axis of the baille structure. In

some cases, the corresponding baille plates of the several plate sets are disposed in parallel planes. In other cases,

the corresponding baille plates are disposed in planes which are inclined at various angles to one another.

In use, a baille structure according to the invention is axially inserted into -a iluid conduit and attached to or otherwise secured against axial movement therein. As will be seen later, a unique feature of at lea-st one form of the present baille structure is that iluid pressure acting axially on the baille tends to Ilock'the latter in fixed position. Fluid flowing through the conduit initially impinges the undersurfaces of the baflle plates of the iirst or upstream baille plate set and is diverted by such baille plates, and the surrounding conduit wall, in a generally spiral flow pattern into the spaces between the baille plates of the iirst and second baille plate sets. The baille plates of the latter sets then continue to divert the fluid in a spiral ilow pattern into the spaces between the baille plates of the second and third baille plate sets, such action continuing until the iluid iinally emerges from the downstream end of the baille structure. As a result of the deflection of the iluid stream by the baille i struct-ure, therefore, the iluid is caused to flow along a generally spiral or helical ilow path through the conduit. Actually, the baille structures of the invention define, in effect, multi-.spiral configurations which induce ilow of the iluid along two or more separate spiral ilow paths. As a consequence of this multi-spiral configuration and the wide open construction of the baille structures and the inclination of the baille plates, the back pressure produced by the baille structures is relatively slight.

In practice, the spiral or swirling motion of the lluid which is induced by the baille structures of the invention may be for the purpose of increasing the effective length of the ilow path of the iluid through the iluid conduits in which the structures are located, or to subf ject the iluid to a centrifugal force, or for a combination of these two purposes. The baille plates of the present baille structures are also uniquely designed to effect a scrubbing action on heat insulating boundary layers on bailles or conduit surfaces in some applica* tions and, in other applications, to reilect incident acoustic wave energy contained in the ilui'cl. In some cases, the baille plates may be perforated to create diffusion of the fluid and/or acoustic energy in the fluid. The baille plates may also be acoustically treated to absorb incident acoustic wave energy or they may be treated with a mechanical filtering material, constructed of fine wire mesh, and/or be otherwise constructed to effect mechanical filtration of the iluid ilowing over the bailles.

The present spiral-ilow-inducing baille structures have general utility and may be used Wherever it is desirable or essential to cause a iluid to follow a spiral ilow path. In order to facilitate .a complete understanding of the invention, however, certain specific applications of the present baille structures are disclosed herein, to wit, a static centrifugal separator, a muiller, an acoustic attenuator, or illter, and a heat exchanger. Numerous other applications of the baille stluctures will immediately occur to those skilled inthe art. Accordingly, it should be understood, at the outset, that these disclosed applications and embodiments of the invention are intended to be illustrative and not limitative of the invention.

A better understanding of the invention may be had from the following detailed description thereof, taken in connection with the annexed drawings, wherein:

FIG. 1 is a perspective view, partly in section, of a static centrifugal separator embodying a spiral-ilow-inducing baffle structure according to this invention;

FIG. la is an enlarged perspective view of the spiralilow-inducing baille structure embodied in the separator of FIG. l;

FIG. 2 is an enlarged section taken on line 2-2 in FIG. l;

FIG. 3 is a longitudinal section through a muiller embodying a spiral-ilow-inducing baille structure according to this invention;

FIG. 4 is an enlarged .perspective of a portion of the baille structure embodied in the muiller of FIG. 3;

FIG. 4a illustrates a baille structure according to the invention having curved baille" plates;

FIG. 5 illustrates an alternative baille structure according to the invention;

FIG. 6, 7 and 8 illustrate portions of baille structures according to the invention in which the baille plates are disposed at dillerent angles to the axes of the structures;

FIG. 9 illustrates an acoustic filter embodying a modilied baille structure according to the invention; and

FIG. l0 is a longitudinal section through a heat exchanger embodying a baille structure according to the invention. f

Referring now to these drawings, and particularly to FIG. 1 thereof, the illustrated centrifugal separator 10 comprises a lbody 12" including an outer, generally cylindrical housing 14. Within this housing is a chamber 16 which opens through the upper end of the housing, as the latter is viewed in FIG. 1. A removable cap or cover 18, releasably held in position in any convenient Way, as by screw threads 2i), normally closes this open upper end of the housing. A seal (not shown) may be provided to seal against fluid leakage between the housing and cover.

The lower end of the housing .14 is closed by an end wall 26. Leading from this end wall, in a generally tangential direction of the housing14, is an outlet 28. The interior passage 30 in this outlet opens'generally tangentially to the lower end of the chamber 16 through the end wall 26 thereof. Rising coaxially through the chamber 16, from the lower end wall 26, is a perforate cartridge supporting sleeve 32. The upper end of this sleeve is open and terminates a distance below the cover 18. The lower end of the sleeve 32 continues in a c0nduit 34 which extends through the bottom Wall 26 of the housing and the wall of outlet 28 and terminates in an external inlet 36. Inlet 36 extends generally radially of the housing 14 in a direction opposite to the direction of extension of the outlet 28. The interior passage 38 of the inlet opens to the lower end of the perforate sleeve 32. The inlet and outlet may be terminally threaded, as shown, for `connection to fluid lines (not shown). y

Slidably fitted on the perforate supporting sleeve 32 is a disposable collector cartridge 40. Cartridge 40 comprises a perforate inner wall 42, an imperforate outer wall 44, and a fibrous filler material 46 between the inner and outer walls 42 and 44. The perforations in the sleeve and the inner wall 42' of cartridge 40 preferably comprise circumferentially extending slits, as shown.

In operation, rfluid to be filtered enters the separator 10 through the inlet 36 and flows upwardly through the perforate cartridge supporting sleeve '32. T-he fluid emerging from the upper end of the sleeve 32 then flows downwardly through the annulus between the wall of the housing 14 and the outer surface ofthe cartridge 40, finally exhausting from the separator through the outlet 28.

Positioned within the cartridge supporting sleeve 32 is a helical-flow-inducing baffle structure 43 which is uniquely constructed in accordance with this invention to cause the fluid to flow upwardly through the supporting sleeve 32 in a spiral or helical flow pattern. As a consequence of this spiral flow, the fluid is subjected to a centrifugal lforce which tends to drive the more dense entrained substances in the fluid toward the perforate wall of the supporting sleeve 32. These substances pass through the perforations in the wall of the sleeve and the perforations in the inner wall `42 of the cartridge 40 and collect in the interior of the cartridge. `In this way, en`

trained liquids or liquid particles can be separated from lgases or vapors, entrained nely divided solid matter or seamos C9 particles can be separated from either liquids or gases, fluids of different densities may be separated, and so on. It is also thus possible to separate particles of solid matter of different densities which are blown through the separator.

rThe spiral-fiow-inducing baffle structure 43 will be seen to comprise a multiplicity of baffle plate sets or pairs 54 disposed in spaced relation along the axis of the cartridge supporting sleeve 32. Each plate pair includes two opposing `baffle plates 54a and 54h located at opposite sides of a first plane i), containing the central axis A of the baffle structure 48. The plates of each such pair have opposing edges 55 located approximately in the latter plane.

The baffle plates of each baffle pair are located in planes which intersect one another, as shown. According to the preferred practice of the invention, these planes of the baffle plates are normal to the axial plane P1 and are equally inclined to opposite sides of a second plane P2 normal to the plane P1 and containing the baffle axis A. The opposing edges 55 of each pair of baffle plates 54a, 54h intersect approximately on the sleeve axis, as shown in the drawings.

In the baffle structure 48 under consideration, the several baffle plates 54a are located in spaced parallel planes, as are the several baffle plates 5417, as clearly shown in FIGS. l and la. Also, the lower tips of the baffle plates of each plate pair 54) abut and are suitably joined, as by integral molding or casting, or by soldering, welding, cementing7 or the like (depending upon the cornposition of the baffles), to the upper tips of the plates of the adjacent lower plate pair. Similarly, the upper tips of the baffle plates of eac-h baffle plate pair correspondingly abut and are joined to the lower tips of the plates of the adjacent upper plate pair. As will be seen later, however, in some applications of kthe invention, only one plate pair may be used or, where several plate pairs are employed, adjacent pairs may be axially spaced and the plates of one pair may not parallel the respective plates of the other plate pairs.

The 'baffle plates 54a and 54h, when viewed in the axial direction of the cartridge supporting sleeve 32, as in FIG. 2, are seen to occupy the entire cross-sectional area of the passage through the sleeve. Since this passage is circular, it is evident that each baffle plate 54a and Sab is one-half of an ellipse, the major axis of which lies in the common plane of the opposing edges of the baffle plates.

For reasons which will appear shortly, it is desirable to have the entire baffle structure 48 rotatably mounted in the cartridge supporting sleeve 32. To tins end, the baffle structure is fixed to a central supporting shaft 53 which projects through the housing cover 21.3 and mounts a knurled grip ai) by which the shaft may he turned to rotate the baffle structure in the supporting sleeve 32. The shaft is sealed to the cover to prevent fluid leakage therebetween. The lower end of the shaft 53 is journaled in a cross member 62 extending across and joined to the lower end of the sleeve 32. A thrust shoulder (not shown) may be provided on the shaft 58 below the cover 18 to restrain the baffle structure against upward axial movement. The baffle structure preferably has a light friction 'fit in the sleeve 32 for restraining t-he structure against rotation under the action of fluid flowing through the sleeve, and for other reasons to be seen shortly.

In operation, fluid flowing through the seperator 10, in the direction described earlier, passes upwardly through the cartridge supporting sleeve 32 and over the baflie structure 48 therein. Upon encountering the first, or lowermost, hafiie plate pair 54, one-half yof the fluid stream imp'inges the undersurface of the bafiie plate 54a divert the respective portions of the fluid stream in an upward and circumferential direction of the sleeve 32, thereby imparting to the fiuid an initial upwardly spiraling flow direction. One-half of the fiuid stream fiows from the underside of the first b'afiie plate 54a around and upwardly in the sleeve 32 into the space between the first and second bafiie plates Srtb, and the other half of the fluid stream fiows from the underside of the first baffle plate 54h around and upwardly into the space between the first and second baffle plates 54a. The first and second baiiie plates 54a and the first and second bafiie plates 5411, and the surrounding wall of sleeve 32, then continue to direct the respective portions or the iiuid stream in upwardly spiraling paths i-nto the spaces 'between the second and third bafiie plates 54a and the second and third bafiie plates 54h, respectively. Similarly, the latter baffle plates continue to direct the fluid in upwardly spiraling paths into the spaces between the `third and fourth bafiie plates 54a and the .third and fourth baffle plates 541;, and so on, until the iuid finally emerges from the upper end of the bafiie structure.

It is evident, therefore, that the baiiie structure 4S acts to direct the fiuid flowing upwardly through the cartridge supporting sleeve 32 in an upwardly spiraling flow pattern, whereby the fluid is subjected to a centrifugal force which is effective to drive the more dense substances, such as foreign matter, entrained in the fiuid radially outward toward 4the wall of the cartridge supporting sleeve 32 and finally through the perforations in the latter sleeve into the collector cartridge 40, all in the manner discussed earlier. It is to be noted that the baffle structure 48 defines, in effect, a double-spiral or double-helix structure, whereby fiuid fiowing through the cartridge supporting sleeve 32 is directed upwardly along two spiraling fiow paths I and II. Because of this double spiral configuration and the wide open construction of the baffle structure, the total effective fiow path area through the baffle structure is substantially increased with respect to a typical conventional single spiral structure for inducing spiral liuid fiow, and the pressure drop 'along the present bafiie structure is substantially reduced with respect to the pressure drop which occurs along such a conventional helix structure. The present baffle structure, therefore, creates substantially less back pressure in the fluid than a conventional helical bafle structure.

When it becomes necessary to replace or clean the cartridge 40, the latter can be simply removed from the housing 14 by removing the cover 18 and baflie structure 48 and then sliding the cartridge upwardly from its supporting sleeve 32. It is also desirable to periodically scrape any accumulations of matter from the inner surface of the cartridge supporting sleeve 32. This is accomplished by turning the grip 60 to rotate the baffle structure 48 in the sleeve, thereby to cause the baffle plates 54a and 54b to scrape the inner surface of the sleeve.

It is obvious that the present baflie structure 48 appreciably increases the overall length .of the effective flow path of the fluid through the cartridge supporting sleeve 32, as compared to the axial length of the sleeve, for example. In this way, the effective residence time of the fiuid in the separator is substantially increased, whereby the efliciency of the separator 10 is appreciably improved. While the baffle structure has been illustrated as having fiat bafiie plates 54a, 54b, curved baiiie plates may be used in some cases, as suggested in FIG. 4a, for example.

The muflier illustrated in FIG. 3 is of the so-called straight-through type and comprises an outer mufiier housing 102 which may be cylindrical, elliptical, or any other shape in cross section, in accordance with conventional muffler practice. Extending through the muffler housing is an exhaust conduit or pipe 104, the ends of which project a distance beyond the ends of the housing for connection in the exhaust line from an internal combustion engine, or other device requiring ya muiller. The muiller shown in FIG. 3, for example, is particularly designed for use on an automotive Vehicle. The ends of the muiller housing 102 are closed by end walls 106 which are welded or otherwise joined to the exhaust pipe din the usual way.

The portion of the exhaust 'pipe 104 contained within the muiller housing 102 is perforated. The perforations 108 in the pipe may be of any suitable shape and arrangement. The annular space 110 between the muffler -housing 102 and the exhaust pipe 104 defines an acoustic attenuation chamber which is acoustically treated or constructed in any of the well-known ways to eilect acoustic attenuation of the acoustic energy waves which are reilected into the chamber in the manner discussed below. For simplicity, the acoustical treatment of the chamber 110 in the illustrated muiller comprises, simply, an -acoustically absorbent material 112. Such an acoustical treatment is most effective for high frequency attenuation. Alternatively, the acoustic chamber 110 of the muiller may be axially divided into separate chambers by partitions of different axial spacing for attenuating specic acoustic frequencies. Such an acoustical treatment is most eillcient for low frequency attenuation. A combination of these two common types of acoustical treatments may be used in the muiller to effect broad band attenulation.

The acoustic energy waves present in the exhaust gas ilowing through the muiller are reilected into the acoustic attenuation chamber 110 by a baille structure 114 constructed in accordance with this invention and positioned in the exhaust pipe 104. This baille structure is essentially identical to the baille structure in the separator of FIGS. 1 and 2 and comprises axially spaced baille plate pairs 116, each including a pair of angularly disposed baille plates 11641 and 1Mb.

The baille structure 114, like the baille structure 48 in FIGS. 1 and 2, denes, in effect, a double-spiral structure, which, in the muiller of FIG. 3, induces spiral or helical flow of the exhaust gas passing through the exhaust pipe 104. As a result, the effective length of the ilow path of exhaust gas through the muiller 100 is substantially greater than the length of the exhaust gas llow path through a conventional straight-through muiller. In

this way, the effective residence time of the exhaust gas within the muiller is increased with respect to the residence time of the exhaust gas in the conventional straightthrough muiller, whereby superior acoustic attenuation is attained in the present muiller without substantially increasing the back pressure.

It .is also evident, of course, that the swirling motion of the gas within the exhaust conduit 104 creates a centrifugal force on the gas which drives the more dense substances in the gas, such as carbon particles, radially outward through the perforations 108 in the exhaust pipe 104 into the acoustic attenuation chamber 110. Thus, the exhaust gas emerging from the present muiller is appreciably cleaner than the exhaust gas emerging from a conventional muffler. Moreover, sparks entrained in the exhaust gas are thus trapped and quenched in the muffler, therby avoiding the possibility of such sparks creating fires, as has been known to ocur. Moisture entrained in the exhaust gas is also driven, by centrifugal force, into the acoustic chamber 110. If desired, the muiller housing 102 may be provided with an opening (not shown) to permit such moisture to drain from the chamber.

In the case of the illustrated muiller, the baille structure 114 serves the additional function of reflecting acoustic enregy waves present in the exhaust gas into the acoustic chamber 110, wherein such waves are absorbed or otherwise attenuated. Thus, the acoustic energy or pressure Waves contained in the exhaustgas ilowing through the muffler expand or travel both radially outward toward the perforated wall of the exhaust pipe 104 and axially through the pipe in the direction of exhaust gas flow therethrough. A portion of the radial wave components, of course, passes through the pipe perforations 108 into the acoustic chamber 110, wherein the waves are absorbed or otherwise attenuated. The axial components of the acoustic waves, on the other hand, impinge the inclined baffle plates 116:1 and 116b of the baille structure 114 and are reflected therefrom toward the perforated wall of the exhaust pipe, as indicated by the arrows in FIG. 3. A portion of this reilected wave energy travels through the pipe perforations 10S into the acoustic chamber 110 and is therein absorbed or attenuated like the radial wave components. It is to be noted that the reflection of acoustic wave energy occurs in two opposing directions from the baille structure 114. Thus, the baille plates 116:1 reflect the incident acoustic wave energy upwardly in FIG. 3, while the baille plates 116b reilect the incident acoustic wave energy downwardly.

The illustrated muiller is, therefore, uniquely arranged to effect superior attenuation of the acoustic wave energy present in the exhaust gas as compared to the acoustic attenuation which occurs in the conventional straightthrough muillers. One weil-known advantage of such a mufller, of course, is that it creates less back pressure than the labyrinth-type muiller, wherein exhaust gas is forced to traverse a zigzag or other circuitous path. As discussed earlier in connection with the centrifugal separator of FIGS. l and 2, the present baille structure, defining a double spiral, as it does, effects gas ilow along two spiral paths with the result that the back pressure of the `gas is increased only slightly by the present baille structure, as compared to the conventional straightthrough -muiller and is substantially less than the back pressure created by a conventional labyrinth-type muiller. The baille structure 114, when viewed in the axial direction of the muiller, completely blocks the line 0f sight through the rnuiller, in the same way as does the baille structure 48 in FIG. 2. As a result, there is no possibility of acoustic pressure waves traveling axially through the exhaust pipe without encountering a reilection toward the surrounding acoustic attenuation chamber 110. In the existing straight-through muiller, of course, acoustic pressure waves can travel axially through the exhaust pipe of the mufiler.

The baille plates 116 and 116b of the baille structure 114, while shown as tlat, may, in some cases, be curved. FIG. 4a illustrates a baille structure 150 having such curved baille plates 152a and 152b. Curved baille plates may be useful, for example, to effect reilection of acoustic wave energy at different angles from different parts of the plates, as indicated by the arrows in FlG. 4a, thereby to break up the acoustic wave pattern in the exhaust gas. Also, acoustic waves which arrive at each such curved plate at various angles of incidence are reflected into the acoustic attenuation chamber 110 of the muiller. The curvature of the bailles may also serve, in some cases, to reduce the air :flow resistance through the baille structure. The baille plates may, in some cases, also be perforated, as shown at 118 in FIG. 4, to eiect diffusion of the exhaust gas and/or `the acoustic wave pattern in the exhaust gas. Such perforations, for example, diiluse the low frequencies, and tend to shift the frequencies present to a higher frequency range wherein attenuation is more easily accomplished. The acoustic attenuation eiliciency of the mufller can be further improved by coating the baille structure with a suitable acoustically absorbent material or providing the baille structure with other acoustic treatment.

In the muiller illustrated in FIG. 3, the baille structure 114 comprises a single integral unit in which all of the baille plates 16a are parallel to each other and inclined at the same angle to the longitudinal axis of the exhaust pipe 104, as are the bafile plates 116D. FIGS. 6-8 illustrate baille structures with baille plates set at different angles. In these iigures, acoustic energy waves present in the iluid ilowing over the baille structure have been depicted b-y arrows to illustrate how changing the angles of the baille plates of a present baille structure changes the angle of reilection of acoustic waves from the plates, thereby to vary the acoustic attenuation eiliciency of the muiller at diilerent acoustic frequencies. It is to be noted here that baille plates which are set at a large angle with respect to a plane normal to the axis oi the baille structure, as are the baille plates in FIG. 8, oiler less resistance to iluid ilow, and, therefore, create less back pressure, than baille plates set at smaller angles, that is, more nearly normal to the baille axis, as are the baille plates in FIGS. 6 and 7. On the other hand, baille plates set at larger angles, as in FIG. 8, increase the length of the ilow path. This design factor may be advantageously employed in all applications of the invention.

In some cases, several individual baille plate pairs,

disposed in spaced relation along the muiller exhaust pipe and having baille plates arranged at different angles to the exhaust stream, may be used. In this regard, FIGS. 6, 7 and 8 can be taken as illustrating successive sections of a unitary exhaust pipe 150 containing such individual baille plate pairs 152, 154 and 156 whose baie plates 158, 160 and 162 are disposed at diilerent angles t-o the direction of exhaust gas ilow.

1 The bale structure 48 in the centrifugal separator of FIGS. 1 and 2 and the baille structure 114 in the muiller of FIG. 3 can be made in various ways. For example, these baille structures may be molded or die cast. Alternatively, the baille plates of these structures may be stamped out of sheet material or may be otherwise separately formed and then joined tip-to-tip and edge-to-edge to form a baille structure. Wher-e the baill-e structure surrounds a separate shaft or tube, or the like, as in 'the case ofthe baille structure 48 of FIGS. 1 and 2, the baille plates may be individually attached to the shaft or tube rather than to one another.

FIG. illustrates a further alternative method of forming a baille structure according to the invention. In this case, the baille structure 200 is composed of identical blanks 202 which may be stamped from sheet material, for example. Each blank 202 comprises lobes or baille plate sections 204 which are located alternately on opposite sides of the longitudinal centerline of the respective blank. The tips of adjacent baille plate sections or lobes 204 are joined by narrow connecting portions 208.

yBlanks 202 are fashioned into a baille structure by bending the blanks at the connecting portions 208 thereof into the sawtooth, zigzag, or sinusoidal conilguration illustrated and then intertwining the blanks, as shown, so that the opposing edges of opposing baillle plate sections 204 abut and intersect one another. These edges of the baille plate sections may be notched, as shown at 210, to effect interlocking of the blanks during assembly. After assembly, the opposing edges of the baille plate sections may be joined where they cross, as by welding, to form a completed structure. When this baille structure is placed in a iluid conduit, pressure of iluid against the structure tends to expand the latter against the conduit wall to eilect selflocking of the baille structure in the conduit. The same applies to the baille structure 114 of FIGS. 3 and 4. i In each of the baille structures discussed thus far and hereinafter described, the particular shape of the individual baille plates, that is, whether these plates are semielliptical, as shown in FIGS. 1-5, or some other shape, depends upon the cross-sectional configuration of the conduit or pipe in which the baille structures are to be used. For example, in a square c-onduit, the baille plates may be rectangular in shape.

The baille structures of the invention may be made of various materials, such Vas metal, plastic, wood, liber glass, wire mesh, etc., depending upon the characteristics of the iluid with which the bafile structures are to be used 10 and the particular functions to be performed by the baille structures in addition to inducing spiral iluid ilow, i.e., acoustic energy reilection, mechanical illtration, acoustic energy absorption, and so on. It will be further immediately evident to those skilled in the art that while the baille structures described thus far dene, in eilect, doublespiral or double-helix structures, it is quite possible to provide additional baille plates and arrange the several baille plates in such a way as to form a triple-spiral, for example. In this case, of course, the edges of the several baille plates would be located in three angularly disposed planes rather than in a common plane, as in the case of the illustrated baille structures.

FIG. 9 illustrates an acoustic attenuator, or sound iilter, 300 according to the invention. This lter comprises a rectangular box-like housing 302 having a rectangular passage 304 therethrough. Within this passage is a baille structure 306 comprising baille plate pairs 308, each including crossed, ilat, rectangular baille plates 308a and 308b. This modified baille structure obviously deiines, in eilect, a double-spiral structure, similar to the baille structures described earlier. Baille structure 306 induces helical ilow of the iluid passing through the iilter and reflects acoustic wave energy present in the iluid toward opposing walls of the iilter housing 302. These housing walls are lined with or composed of an acoustically absorbent material which absorbs the incident wave energy. The baille structure may also comprise or be coated with an acoustically absorbent material.

This type of acoustic iilter, or attenuator, is useful, for example, in an air duct of an air conditioning system to deaden noise. The primary purpose of inducing spiral iluid ilow in the illustrated iilter is to increase the eilective length of the ilow path of iluid through the iilter and, thereby, the effective residence time of the iluid in the lter without appreciably increasing back pressure. In this way, maximum acoustic attenuation is attained. It is possible, however, that such a illt-er could have perforated acoustically absorbent walls surrounded by a collection chamber for collecting dust and other foreign matter entrained in the iluid and which is driven through the perforations of the walls by centrifugal force, as in the earlier described devices according to the invention.

The heat exchanger 400 shown in FIG. 10 comprises an outer casing 402 having a iluid inlet 404 at one end and a iluid outlet 406 at the other end. Extending axially through the casing is a iluid conduit 408, having a iluid inlet and outlet at opposite ends. Mounted within the casing 402, about conduit 408, is a baille structure 410. Baille structure 410 comprises, in a manner similar to the earlier baille structures, a succession of baille plate pairs 412, each including a pair of crossed baille plates 412a and 412b. These baille plates may be ilat, as in FIG. l0, or curved, for example, as suggested in FIG. 4a. Within the conduit 408 is a second baille structure 414 having a succession of baille plate pairs 416 including crossed baille plates 416a, 416b.

In this case, the baille structures 410 and 414 induce spiral ilow of iluid about the outside of and within the central iluid conduit 408, thereby to increase the efiective lengths of the iluid ilow paths through and about the exterior of the` iluid conduit 408. The resultant swirling of the iluid within and about the conduit also eilects scrubbing away of the stagnant, thermally insulating boundary layers of iluid existing at the inner and outer surfaces of the conduit 4.08, thereby substantially improving the coeilicient of heat transfer between a iluid ilowing through the conduit 408 and a iluid ilowing through the casing 402. Such a heat exchanger is useful, of course, to eilect heat exchange between any two iluids, one of which enters the exchanger through the inlet 404 and exhausts from the exchanger through the outlet 406, and the other of which iluids enters the heat exchanger through one end of the central iluid conduit 408 and exhausts from the heat exchanger through the other end of the conduit. The hotter of the two iluids may, obviously, be directed either through the casing 402 or through the conduit 404. The use of two baffle structures in the heat exchanger, one within and the other about the central conduit 408, is optional since good heat exchange between the fluids flowing through the exchanger can be attained by the use of either baille structure alone.

The heat exchange apparatus of FIG. is generally illustrative of the use of my spiral-ilow-inducing bailles in heat exchangeapparatus. The specific apparatus of FIG. 10, however, is not to be taken as limitative in any sense on the broad invention. Various combinations of iiuids may be used in the apparatus. Thus, hot air may be used within the fluid conduit, to heat water in the outer conduit. As another possibility, hot air within the conduit may heat a larger volume of hot air in a large chamber outside the conduit, as in a forced air :heat exchange system. Thus, for example, gas-heated air and combustion products may be conveyed through a vertical conduit equipped with my baille structure. Outside this conduit, air to be heated may be circulated, either longitudinally of the conduit, or laterally thereof, and this latter air may be forced to ilow past the outside of the conduit by a suitable blower, and may be conveyed away to a place of utilization.

It will be seen that the baille structures of the invention are especially advantageous in heat exchanger apparatus. They provide, iirst, long ilow paths along the tube Walls. These ilow paths may be made quite long by arranging the baille plates at large angles to the tube axis. Second, they assure exceptionally good mixing of the fluid, and thus good temperature distribution, whereby the iluid ilowing adjacent the walls is at optimum temperature. Third, they assure vigorous scrubbing of the spiral ilow iluid against the surfaces of the conduit, as Well as, in fact, against the baffles themselves, thereby removing the heat insulating boundary layers, which has the effect of improving heat transfer performance, as well as reducing boundary layer drag on the fluids flowing along the conduit walls and along the bailles.

It is evident from the preceding description that one highly unique and desirable feature of the present spiralilow-inducing baille structures resides in their essentially wide open, multi-spiral configuration which presents maximum, effective ilow path area and thereby minimum resistance to fluid flowing through the baffle structures. As a consequence, the baille structures create minimal back pressure in the lluid. As noted earlier, the back pressure created by the present baille structures can be further reduced by increasing the angle of the baille plates.

Another important feature of the invention resides in the fact that the effective length of the spiral fluid ilow paths through the present baille structures is substantially increased with respect to the axial length of the structures without creating any substantial back pressure in the fluid stream in which the baille structures are located. Depending upon the diameter and angle of the baille plates, for example, the effective length of the spiral ilow paths through a present baille structure may be double or triple the axial length of the baille structure. Such increased flow path length is advantageous for the reasons discussed earlier.

Clearly, therefore, the invention herein described and i1- lustrated is fully capable of attaining the several objects and advantages preliminarily set forth.

While certain presently preferred embodiments of the invention have been disclosed, these embodiments are intended to be illustrative rather than limitative of the invention and are presented merely to facilitate a complete understanding of the invention. It is to be distinctly understood that many additional uses of the baille structures of the invention are envisioned and may be found, including uses such as for guiding ionized gases, electron streams, or for any other purpose wherein they may fuliill a useful function.

Accordingly, it is to be understood that various modifications in the design, arrangement of parts, instrumentalities and applications of lthe invention are possible within the spirit and scope of the following claims.

I claim:

1. An exhaust muiller, comprising:

a muiller housing;

a perforate exhaust pipe extending through said housing, there being an exhaust passage in said pipe;

a series of baille plate pairs mounted in said pipe in spaced relationship along the longitudinal axis of said pipe;

the two baille plates of all of said pairs being located predominantly on opposite sides of a common longitudinal plane through said axis, and being arranged to cross one another substantially at said axis and at opposite acute angles to said plane, said crossing plates having inner edges in proximity to said plane and outer edges substantially adjacent to the inner surface of said pipe, each baille plate of a given pair terminating longitudinally of the pipe in an extremity which lies adjacent to the extremity of that baille plate of the next succeeding pair which is on the opposite side of said longitudinal plane,

said crossing baille plates affording two unobstructed spiral gas passages turning about one another, and affording also a succession of acoustic reilecting surfaces diagonally across the cross-sectional areas of said pipe which are on opposite sides of said longitudinal plane, whereby acoustic waves traversing said pipe encounter said reilecting surfaces and are thereby directed outwardly toward the perforate wall of said pipe.

2. The subject matter of claim 1, wherein said baille plates contain multiple perforations.

3. The subject matter of claim 1, wherein at least some of said baille plates are curved in the region of their extremities.

4. The subject matter of claim 1, wherein the baille plates of different baille plate pairs are disposed at different angles to the longitudinal axis of the pipe.

5. In an acoustic wave absorber, the combination of a conduit bounded by acoustically absorbent means;

a series of baille plate pairs mounted in said conduit in spaced relationship along the longitudinal axis of said conduit;

the two baille plates of all of said pairs being located predominantly on opposite sides of a common longitudinal plane through said axis, and being arranged to cross one another substantially at said axis and at opposite acuate angles to said plane, said crossing plates having inner edges in proximity to said plane and outer edges substantially adjacent to the inner surface of said conduit, each baille plate of a given pair terminating longitudinally of the conduit in an extremity which lies adjacent to the extremity of that baille plate of the next succeeding pair which is on the opposite side of said longitudinal plane,

said crossing baille plates affording two unobstructed spiral gas passages turning about one another, and affording also a succession of acoustic reilecting surfaces diagonally across the cross-sectional areas of said conduit which are on opposite sides of said longitudinal plane, whereby acoustic waves traversing said conduit encounter said reilecting surfaces and are thereby directed outwardly toward the boundary of said conduit.

References Cited bythe Examiner UNITED STATES PATENTS 1,833,871 1l/l93l Ewing et al 165-160 X 2,016,341 10/1935 Nelson l38-38 X 2,067,133 1/1937 Wales 138-38 (ther references on following page) 

1. AN EXHAUST MUFFLER, COMPRISING: A MUFFLER HOUSING; A PERFORATE EXHAUST PIPE EXTENDING THROUGH SAID HOUSING, THERE BEING AN EXHAUST PASSAGE IN SAID PIPE; A SERIES OF BAFFLE PLATE PAIRS MOUNTED IN SAID PIPE IN SPACED RELATIONSHIP ALONG THE LONGITUDINAL AXIS OF SAID PIPE; THE TWO BAFFLE PLATES OF ALL OF SAID PAIRS BEING LOCATED PREDOMINANTLY ON OPPOSITE SIDES OF A COMMON LONGITUDINAL PLANE THROUGH SAID AXIS, AND BEING ARRANGED TO CROSS ONE ANOTHER SUBSTANTIALLY AT SAID AXIS AND AT OPPOSITE ACUTE ANGLES TO SAID PLANE, SAID CROSSING PLATES HAVING INNER EDGES IN PROXIMITY TO SAID PLANE AND OTHER EDGES SUBSTANTIALLY ADJACENT TO THE INNER SURFACE OF SAID PIPE, EACH BAFFLE PLATE OF A GIVEN PAIR TERMINATING LONGITUDINALLY OF THE PIPE IN AN EXTREMITY WHICH LIES ADJACENT TO THE EXTREMITY OF THAT BAFFLE PLATE OF THE NEXT SUCCEEDING PAIRWHICH IS ON THE OPPOSITE SIDE OF SAID LONGITUDINAL PLANE, SAID CROSSING BAFFLE PLATES AFFORDING TWO UNOBSTRUCTED SPIRAL GAS PASSAGES TURNING ABOUT ONE ANOTHER, AND AFFORDING ALSO A SUCCESSION OF ACOUSTIC REFLECTING, AND FACES DIAGONALLY ACROSS THE CROSS-SECTIONAL AREAS OF SAID PIPE WHICH ARE ON OPPOSITE SIDES OF SAID LONGITUDINAL PLANE, WHEREBY ACOUSTIC WAVES TRAVERSING SAID PIPE ENCOUNTER SAID REFLECTING SURFACES AND ARE THEREBY DIRECTED OUTWARDLY TOWARD THE PERFORATE WALL OF SAID PIPE. 